This invention relates to ultrasonic imaging systems and methods, and particularly to ultrasonic imaging systems and methods that utilize both harmonic and fundamental imaging modes.
Ultrasonic imaging systems that combine ultrasonic images from multiple transmit beams to form a single improved image are described for example in U.S. Pat. Nos. 5,568,813; 5,111,824; 5,462,057; and 5,579,770. The methods described in these patents however do not address the issue of providing high image quality in harmonic images of technically difficult examinations.
Hossack et al. U.S. patent application Ser. No. 08/638,918, assigned to the assignee of the present invention, discloses a method and system that combine nearfield harmonic imaging and farfield fundamental imaging to create a single improved image. This application also discloses a system and method that combine a nearfield image which is an amplitude matched combination of fundamental and harmonic signals with a farfield fundamental image to form a single improved image.
In spite of the improvements provided in the above identified Hossack application, a need presently exists for an ultrasonic imaging system and method that provide improved nearfield imaging, particularly for use in harmonic imaging systems used to image tissue without added nonlinear contrast agent. In such cases, particularly in technically difficult examinations, the nearfield and farfield performance may be less than optimum because of small nonlinear propagation distances in the nearfield and decreases in the signal to noise ratio in the farfield.